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Fat Thursday | Roman Wrzalik, PhD, DSc, Associate Professor

15.02.2023 - 22:04 update 15.02.2023 - 23:09
Editors: magdakorbela
Tags: save the date

16 February


Save the date with our scientists

„Save the date” is a series of articles that have been written to celebrate various unusual holidays. The authors of the presented materials are students, doctoral students and employees of the Faculty of Science and Technology of the University of Silesia.

Bartek said that today is Fat Thursday…

It is Carnival time, so you can and even should enjoy yourself! And eat, drink and let loose. There will still be time to get back in shape and work on the perfect figure for the summer holidays. We’ll still make it. Unless Fat Thursday drags on a bit, then it can be a problem. But that’s a different field of science.

… and Bartkowa [Bartek’s wife] believed it and she fried some greasy doughnut! [Polish proverb]

Greasy, fragrant, delicious and… calorific. This is less positive information, but a very necessary one! Because if we look at the calories in terms of physical science, it may turn out that we cannot devour doughnuts only with our eyes. What is a calorie? Where did it come from? What is the daily caloric requirement? These questions will be answered by Roman Wrzalik, PhD, DSc, Associate Professor from the Institute of Physics.

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ROMAN WRZALIK, PhD, DSc, Associate Professor

Institute of Physics

A calorie (cal) is a unit of energy. Used in dietetics (more often as kcal, i.e. a kilocalorie, which is 1000 calories), it tells us how much energy our body can obtain from eating a certain amount of food. Looking at a doughnut, someone who is trying to lose weight will say that it is as much as 500 kcal, and they will be tormented by the sight of it on Fat Thursday. Whereas all they should think about is how much of their daily energy requirement that is. When we do not work hard, but, for example, sit at the desk, we need about 1800 kcal, but when we do physical work, we need even up to 3500 kcal a day. So all you have to do is run a bit to be able to eat more doughnuts.

How do we know how many calories a particular product provides the body with? We can determine this on the basis of tables developed by dieticians containing data on the calorific value of simple ingredients, such as sugar, protein or starch.

For a physicist, a calorie (cal) is an auxiliary unit of energy, which can be expressed by the applicable unit with the symbol J – joule. We can easily convert these units, because 1 cal is about 4.18 J. Therefore, nothing stands in the way of expressing the “absorbable” energy of a doughnut in joules. However, it would look worse, because 500 kcal is almost 2092 kJ, and this sounds very dangerous.

Where did the calorie come from? Today, a calorie is defined as the amount of heat needed to heat, under the pressure of 1 atmosphere, 1 g of chemically pure water by 1°C from 14.5°C to 15.5°C. Its history is related to the history of physics, and more broadly, to the development of our knowledge of nature. It was only in the mid-nineteenth century that the knowledge of heat began to be combined with mechanics and the scientists learned that thermal energy, measured by body temperature, is the energy of the movements of molecules and atoms inside the body. In the famous experiment, James Joule (1818–1989), a British physicist, showed that mechanical work can be converted into “heat” (physicists prefer to talk about the internal energy of bodies) and determined the relationship between a calorie and a joule. So he combined the calorie, the unit of “heat”, with the unit of mechanical work, the joule. “Heat” and the energy of motion are therefore different forms of the same energy.

To what conclusion all this information brings us? Today, we should forget about the “cold” and basically emotionless units of energy, and focus our attention on something that evokes so many positive feelings – the doughnut, or rather ‘Mr. Donut – the king of the end of the Carnival’.

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